1. Field of the Invention
The present invention relates to thermoelectric heating and cooling devices. More particularly, the invention relates to a thermoelectric heat pump fluid circuit for alternately delivering hot and cold fluids to a therapeutic heat pad, wrap, or other device.
2. Description of the Prior Art
Many devices and objects must be alternately heated and cooled during their use, manufacture, or maintenance. For example, in sports therapy, it is common to treat injured patients by alternately applying heat and cold to the injuries in a cyclic fashion via a heat pad or wrap. This procedure is commonly referred to as contrast therapy and is considered to be effective in reducing the healing time of an injury. To achieve the best therapeutic results with contrast therapy, it is beneficial to rapidly switch between application of heat and cold and to accurately control the temperature, time and other parameters relating to the treatment.
Prior art devices have been developed to alternately deliver hot and cold fluids to an end device for heating and cooling the end device. These prior art devices typically use thermoelectric heat pumps for heating and cooling the fluid delivered to the end device. Switching from heating to cooling (or vice versa) is accomplished by electrically reversing the polarity of power applied to the heat pump. This causes the hot side of the heat pump to become cold or the cold side to become hot to change the temperature of the fluid passing thereby before it is delivered to the end device. Unfortunately, the thermal mass of the heat pump slows the transition between heating and cooling modes after the polarity of the power has been reversed and therefore significantly limits the cycling speed of these prior art devices.
Electrically switching a heat pump between heating and cooling modes to alternately heat and cool an end device also wastes the heat present on the hot side of the heat pump when it is switched to a cooling mode and wastes the cool produced on the cold side of the heat pump when it is switched to a heating mode. This reduces the efficiency and therefore increases the operating costs of these prior art devices, especially when the devices must be frequently switched between heating and cooling modes as is done in contrast therapy.